Circuit and method for detecting current zero-crossing point, and circuit and method for detecting load voltage

A circuit for detecting a load voltage, comprising:

• a load power supply circuit;
• a voltage-dividing resistor;
• a transistor switch;
• a voltage detection circuit;
• and
• a zero-crossing detection circuit,
• wherein said load power supply circuit comprises a load, a diode, and an inductor, and said load, said diode and said inductor are connected in series to form a ring circuit;
• one end of said load power supply circuit is coupled to an operating voltage input terminal, and the other end of said load power supply circuit is coupled to a first end of said transistor switch and a first end of a voltage-dividing resistor;
• a second end of said voltage-dividing resistor and a second end of said transistor switch are coupled to ground;
• a load voltage is controlled by said transistor switch, and a voltage-dividing terminal of said voltage-dividing resistor is coupled to a signal input terminal of said voltage detection circuit and to a signal input terminal of said zero-crossing detection circuit, said zero-crossing detection circuit is used to determine whether a diode current crosses zero and to obtain an on time of said diode;
• said voltage detection circuit obtains said load voltage by use of a first voltage sampled and maintained at said voltage-dividing terminal, said on time of said transistor switch and said on time of said diode,
• wherein by said zero-crossing detection circuit, a first voltage at said voltage-dividing terminal is sampled and maintained when said transistor switch is turned off and said diode is turned on, a result obtained by subtracting said first voltage by a reference voltage is compared with a second voltage at said voltage-dividing terminal obtained in real time, to determine that a diode current crosses zero in a case that said second voltage is smaller than said first voltage,
• wherein said voltage-dividing resistor is configured to divide voltage of said first terminal of said transistor switch and provide a divided voltage at said voltage-dividing terminal.